1. Field of the Invention
The present invention relates to a tubular connection assembly of metallic risers, such as steel catenary risers and steel lazy wave risers. More particularly, the present invention relates to a tubular connection assembly with improved fatigue performance. Even more particularly, the present invention relates to a tubular connection assembly with flared and thickened ends.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
A steel catenary riser (SCR) or steel lazy wave riser (SLWR) is pipeline comprised of rigid, steel pipes or tubular welded end to end to each other. An SCR connects a pipeline on the seabed to a floating or fixed oil and gas production platform. Fluids, like oil, gas, injection water, etc. are transported between the platform at the surface and the pipeline on the seabed.
The SCR and the SLWR are well known in the offshore industry. The SCR or SLWR hangs down from the floating or fixed platform and into the sea. The SCR shape looks like a curve of a catenary equation in the field of mathematics, hence the term “catenary” in the name of this type of metallic riser. The shape is controlled mainly by water depth and hang-off angle. The SLWR has a buoyancy portion so that there is bend in the curve between the platform and the seabed. The SLWR shape is controlled mainly by water depth, hang-off angle, and buoyancy.
The pipes of the SCR and SLWR are connected by conventional welding techniques. The welds between pipes or tubulars are more critical for fatigue performance than the respective bodies of the pipe. The strength and quality of the welds are directly related to the working life of the SCR and SLWR.
Cyclic loading on the pipes or tubulars of metallic risers, such as SCRs, SLWRs, and top tensioned risers, results in cyclic stresses that lead to fatigue damage, and, given sufficient time, to fatigue failure. The amount time for fatigue failure is typically referred to as the fatigue life. Resistance to fatigue damage is known as fatigue performance. The location where tubulars are welded together is more critical than the body of the tubular and has shorter fatigue life. The cyclic stresses are proportional to the diameter and wall thickness of the tubular. For a given cyclic loading, the cyclic stresses decrease as the wall thickness or diameter increases. As such, there is improved fatigue performance and longer fatigue life, as the wall thickness or diameter increases.
Various patents and publications have disclosed inventions related to metallic risers. Upset ends or thickening of the end of the pipe are well established as means for improving welded connections of adjoining pipes. U.S. Pat. No. 2,258,751, issued to Evans on Oct. 14, 1941, teaches a method of making welded tool joints whereby the wall thickness of the pipe at the weld point is increased by machining the weld to a greater thickness. The thickness is at least equal to a thickened end of an adjacent pipe. The object of the invention is to increase the strength at the weld point by increasing the thickness. The figures demonstrate the thickened wall aspect of the invention at the weld point. The internal diameter of the pipe is constant.
U.S. Pat. No. 3,458,922, issued to Schellstede, et al. on Aug. 5, 1969, teaches a method of constructing a drill pipe protector. Pipe with thickened or upset ends are welded together. The welded ends form an integral collar, which protects the drill pipe. According to the figures, the pipe retains the same diameter within the joined pipe.
Japanese Patent No. 361086028, issued to Hashimoto, et al. on May 1, 1986, discloses the method for production of plate rolled steel pipe with a thickened end part. The inner diameter of the pipe is fixed, but the outer diameter at the end portion of the pipe shaft is produced by plate rolling a steel plate of a different thickness. The resulting thickened end may then be welded to an opposing end of a second to create a joint.
U.S. Pat. No. 7,282,663, issued to Alford, et al. on Oct. 16, 2007, teaches an automated forge welding method, which may be used to join pipe ends in a welding chamber while the ends are maintained, aligned, and parallel relative to each other. The amount of upset is controlled within a particular thickness range.
Other references continue to disclose the upset ends with further improvements to aspects of the weld, such as male-female connector limitations, axial symmetry limitations and constant diameter of the flow channel limitations.
U.S. Pat. No. 5,562,312, issued to Carlin on Oct. 8, 1996, teaches a system and method for enhancing fatigue and load properties of a drill pipe at the pipe section welds by using helical welding of pipes cut at matching helical angles, instead of circular welding. The stresses at any cross section will be distributed between the weld and the pipe body, the latter usually being stronger. The outer diameters of the pipes are the same.
U.S. Pat. No. 7,897,267, issued to Hoyt, et al. on Mar. 1, 2011, also discloses a system and method of improving riser weld fatigue. In one embodiment, a SCR is formed using riser joints which are bonded together using dissimilar weld material from the pipe sections. The riser joints are provided with a partial cladding which increases the fatigue performance of the weld. FIG. 4 demonstrates that the inner and outer diameters are the same at the weld point, after the welding and cladding processes.
United States Publication No. 20080226396, published for Garcia, et al. on Sep. 18, 2008, discloses a seamless steel tube for use as a SCR with a particular chemical composition and pipe body constructions having a transition zone and an upset end. The transition zone was a symmetric thickening, and the flow channel stayed in the same orientation. FIG. 2 demonstrates the wall thickness at the joint is of a greater external diameter than the rest of the pipe body. The publication discloses restrictive chemical composition limitations.
U.S. Pat. No. 8,783,344, issued to Aung, et al. on Jul. 22, 2014, claims the method of manufacturing a wear resistant drill pipe by joining a first and second drill pipe. Each drill pipe has an upset end at the joining end. The upset ends are substantially equal on both pipes in terms of their external diameter, and the external diameter is greater that then external diameter of the rest of the drill pipe. The increase in external diameter is the product of redistributing a portion of a substrate material at the upset end of the first and second drill pipe. The method of joining the first and second drill pipe at their upset ends may be an inertia welding or friction welding process. The internal diameter remains the same through the drill pipes.
The prior art reduces the cyclic stresses by increasing only the wall thickness for a given diameter. There are limitations on only increasing wall thickness with constant internal diameter or decreased internal diameter to achieve a desired fatigue life and fatigue performance. There are technical limitations on wall thickness due to weld quality. Being too thick can reduce the weld quality, such that the weld would not be sufficient for SCR or SLWR applications. There are practical limitations as well because the welds are performed offshore onboard an installation vessel with costly day rates. A complicated weld process to maintain weld quality reduces the numbers of welds to be completed in one day. The costs for an SCR or SLWR for pipes or tubular with increased thickness can be increased too high for deployment in the field.
It is an object of the present invention to provide a method and tubular connection assembly for metallic risers with improved fatigue performance.
It is an object of the present invention to provide a method and tubular connection assembly for a steel catenary riser or a steel lazy wave riser with more durable welds.
It is an object of the present invention to provide a method and tubular connection assembly for a steel catenary riser or a steel lazy wave riser with cost efficient welds.
It is an object of the present invention to provide a method and tubular connection assembly for metallic risers with flared and thickened ends.
It is another object of the present invention to provide a method and tubular connection assembly for metallic risers with increased internal diameter and increased wall thickness at the weld point for adjoining pipes.
It is an object of the present invention to provide a method and tubular connection assembly for metallic risers with an amount of increased internal diameter at an end related to an amount of increased wall thickness at that end.
It is another object of the present invention to provide a method and tubular connection assembly for metallic risers with fatigue performance improved by increasing internal diameter relative to increasing wall thickness.
These and other objectives and advantages of the present invention will become apparent from a reading of the attached specifications and appended claims.